Chthamalus hedgecocki, Pitombo & Burton, 2007

Pitombo, Fábio Bettini & Burton, Ron, 2007, Systematics and biogeography of Tropical Eastern Pacific Chthamalus with descriptions of two new species (Cirripedia, Thoracica), Zootaxa 1574 (1), pp. 1-30 : 4-8

Chthamalus hedgecocki sp. nov.

( Figures 2–7 )

Type material. Holotype: Adult , 6.4mm, cirri and mouthparts dissected and mounted on one slide, opercular plates and parietes dried. Punta Camarón, Mazatlan, Sinaloa, Mexico (23 0 14’15’’N 106 0 26’45’’W) [MNRJ- 19712]. Collected by F. B. Pitombo and J. S. Barrangán, 18 February 2002, attached to rocks on a waveexposed shore, upper midlittoral zone.

Paratypes: same locality, collector and collection date as holotype. One adult, cirri and mouthparts dissected and mounted on one slide, opercular plates and parietes dried, CO1 gene sequenced [MNRJ-19716]; four adults [MNRJ-19717] with cirri and mouthparts dissected and mounted on one slide each, opercular plates and parietes dried; two adults, specimens not dissected [SIO-BIC C-10941]; two adults, specimens not dissected [EMU-6842] .

Diagnosis. Chthamalus with shell pale brown externally, folds not reaching apex; wall pale brown internally with longitudinal brown ridges near base. Scutum with articular ridge narrow, not projecting beyond tergal margin. Tergum truncate, with spur broad, short; outer face with weak longitudinal furrow close to scutal margin. Cirrus I with row of long setae on outer face of outer ramus, distal article of inner ramus without bidenticulate setae; cirrus II with bidenticulate setae with basal guards on one or sometime two distal articles of inner ramus.

Description. Based on holotype, supplemented with some measurements made of 5 paratypes [MNRJ- 19716 and MNRJ-19717].

Shell: externally pale brown near basis, white on corroded surface, folded in lower half; internally wall with longitudinal brown ridges when cleaned, sheath brown, orifice wide; articulation between scutum and tergum presenting a slight angle; rostro-carinal and orifice aperture diameters 6.4 mm and 2.2 mm, respectively.

Scutum: both plates corroded in upper part, growth lines present only in lower third; length/width ratio of right and left plates 1.9 and 1.8, respectively [avg. of 5 paratypes = 1.7 ±0.2]; plates weakly asymmetric, left plate with tergal margin 5% wider [avg. of 5 paratypes = 7% ±3 of asymmetry, all on left plates]; occludent margin of left scutum with growth lines on inner face occupying 19% its height (right scutum not showing inward growth) [avg. of 5 paratypes = 21% ±2.7]; articular furrow wide, articular ridge short, not reaching tergal margin; adductor muscle ridge weak, not attaining basal margin; lateral depressor muscle pit deep, smooth; sum of occludent angles 135 0 [avg. of 5 paratypes = 131 0 ±8 0]; the ratio between width of adductor muscle insertion and width of scutum at the level of adductor muscle 0.3 for both plates [avg. of 5 paratypes = 0.38 ±0.05].

Tergum: wide with ratio between scutal and carinal margins 0.89 for both plates [avg. of 5 paratypes = 0.87 ±0.07]; scutal margin of left tergum 11% higher than right [avg. of 5 paratypes = 9.6% ±5, 3 higher on right, 2 higher on left plates]; spur short, wide; four tergal depressor muscles crests, extending about 1/4 of carinalt margin; weak longitudinal furrow present on outer face close to scutal border in both plates.

Labrum: with upper margin concave, bearing row of short conical teeth.

Palps: with upper margin covered by single row of short smooth setae proximally and distally towards supero-distal angle, setae lengthening to form clump; very long pinnate setae on distal margin lengthening toward infero-distal angle.

Mandible: quadridentated, with fourth tooth double with row of approximately 18 closely spaced, fine spines below; the lower angle of left mandible with 3 strong spines, right mandible with 1 (2 broken).

Maxilla I: cutting edge with 3 steps; upper angle with pair of developed spines and 1 shorter marginal spine, 4 and 3 slender spines below on right and left maxillae, respectively; notch weak, row of 7 and 8 subequal spines below on left and right maxillae, respectively, lowest spine short, thick, bifid; inferior angle protuberant, covered with row of slender spines, 1 strong spine centrally placed.

Maxilla II: posterior margin of distal lobe covered with long, acuminate finely pinnate setae becoming shorter, smooth, acuminate setae on anterior margin; outer face with patch of very fine setae near distal margin; anterior margin of proximal lobe covered with short setae with very fine pinules not reaching apex.

Cirrus I: right and left cirri composed of 6 (outer) and 5 (inner) articles; inner face of articles of both rami covered with long, acuminate, pinnate setae; outer faces of outer rami with longitudinal row of long setae; inner rami without bidenticulate setae.

Cirrus II: right and left cirri composed of 6 (outer) and 5 (inner) articles; bidenticulate setae with basal guards (complex setae) present on inner faces of distal articles of both cirri; outer rami with 4 complex setae on distal article; right and left inner rami with 3 and 4 complex setae on distal article, respectively; inner faces of articles covered with long, acuminate, finely pinnate setae.

Cirrus III: right cirrus anteniform, composed of 21 (outer) and 14 (inner) articles; left cirrus formed by 19 (outer) and 15 (inner) articles; inner face of outer rami with 4 pair of long setae on 14 (right) and 13 (left) medial articles; inner faces of both inner rami with 5 pairs of long setae on 3 medial articles, short setae between each pair of long setae on protuberance; most distal article of each ramus with group of 3 stout setae distally, feature repeating from cirri IV to VI.

Cirrus IV: right and left cirri for composed of 16 (outer) and 15 (inner) articles; inner faces of both outer rami with 5 pairs of setae on 6 medial articles; inner faces of both inner rami with 5 pair of setae, on 2 (right) and 3 (left) medial articles.

Cirrus V: right cirrus composed of 17 (outer) and 15 (inner) articles; left cirrus with 16 articles on both rami; inner face of both outer rami with 5 pairs of setae on 8 medial articles; inner face of both inner rami with 5 pair of setae, on 7 (right) and 10 (left) medial articles.

Cirrus VI: right cirrus composed of 17 articles on both rami; left cirrus formed of 17 (outer) and 16 (inner) articles; inner faces of both outer rami with 5 pairs of setae on 9 medial articles; inner faces of both inner rami with 5 pairs of setae on 10 (right) and 9 (left) medial articles.

Penis: with genital aperture surrounded by tuft of long setae, 4 longitudinal rows of long setae radially placed on distal third.

Distribution. Punta Lobos, Baja California Sur to Acapulco, Sinaloa, Mexico ( Fig. 8 )

Habitat. Chthamalus hedgecocki is found in the upper midlittoral zone, usually on wave exposed shores, but also found at protected sites.

Remarks. Chthamalus hedgecocki belongs to the C. fissus group as it has bidenticulate setae with basal guards on cirrus II and lacks conical spines on the outer ramus of cirrus I. Within the C. fissus group, the articular ridge not extending beyond the tergal margin is the main feature that distinguishes C. hedgecocki from C. proteus , C. fragilis and C. anisopoma . The form of the tergum, quadrangular in C. hedgecocki and triangular in C. fissus , distinguishes these two species. The presence of a longitudinal furrow on the outer face of the tergum, a feature shared by C. hedgecocki and C. panamensis , distinguish these two species from all others within the genus. However, it is weak in C. hedgecocki , sometimes hardly noticeable in uncleaned shell, whereas C. panamensis shows a well-marked furrow on both plates. These two species live in sympatry from Punta da Mita, Banderas Bay, to Acapulco, Mexico. Chthamalus hedgecocki normally has a brown, smooth shell, with wide folding limited to half the shell height, whereas C. panamensis normally has a brown to white shell with narrow, deep folding extending to the top of the shell. Chthamalus panamensis extends down to the Panamanian coast.

Etymology. Chthamalus hedgecocki is named in honor of Dr Denis Hedgecock for his pioneering work on the variability of the Chthamalus fissus species group and for the discovery of isolated populations that proved to be new species.

Figures

FIGURE 2. Chthamalus hedgecocki sp. nov., holotype MNRJ-19712. Shell with opercular plates not removed. Scale bar = 1mm.

FIGURE 3. Chthamalus hedgecocki sp. nov., holotype MNRJ-19712. Opercular plates. A-D scuta; E-H terga; A,C,E,F left plates; B,D,G,H right plates; A,B,F,G outer face; C,D,E,F inner face. Scale bar 1mm.

FIGURE 4. Chthamalus hedgecocki sp. nov., holotype MNRJ-19712. Left mandible: A- schematic (setae omitted); Bphoto of lower angle. Scale bar = 0.05 mm

FIGURE 5. Chthamalus hedgecocki sp. nov., holotype MNRJ-19712. Right maxilla I: A- schematic (setae omitted); Bphoto of lower angle. Scale bar = 0.050 mm

FIGURE 6. Chthamalus hedgecocki sp. nov., holotype MNRJ-19712. Left cirrus II. A- schematic (setae omitted); Bschematic of inner ramus distal segments showing only the bidenticulate setae; C- photo of inner ramus distal segments. Scale bar: A = 0.2 mm; B and C = 0.05 mm.

FIGURE 7. Chthamalus hedgecocki sp. nov., holotype MNRJ-19712. Cirri III and VI. A- schematic of cirrus III, right (setae omitted); B- schematic of cirrus VI, right (setae omitted); C- schematic of sixth and seventh segments of cirrus VI outer ramus. Scale bar A and B = 0.2 mm; C = 0.05 mm.

FIGURE 8. Distribution of Chthamalus hedgecocki sp. nov., C. panamensis Pilsbry and C. dalli Pilsbry along the western coast of the Americas. Symbols mark the localities from where specimens were examined; encircled symbols indicate localities where the COI gene was sequenced.